This section provides background information related to the present disclosure which is not necessarily prior art.
The automobile industry is actively working to develop alternative powertrains in an effort to significantly reduce or eliminate the emissions exhausted into the air by conventional powertrains equipped with an internal combustion engine. Significant development has been directed toward electric vehicles (EV) that are equipped with one or more electric traction motors. For example, some electric vehicles are only powered by the electric motor(s) and rely solely on the electrical energy stored in an on-board battery pack. However, some other electric vehicles, commonly referred to as hybrid electric vehicles (HEV), have both an internal combustion engine and one or more traction motors.
There are two types of hybrid electric vehicles, namely, series hybrid and parallel hybrid. In series hybrid electric vehicles, tractive power is generated and delivered to the wheels by the electric traction motor(s) while the internal combustion internal combustion engine is used to drive a generator for charging the battery pack. In parallel hybrid electric vehicles, the traction motor(s) and the internal combustion engine work independently or in combination to generate and deliver tractive power to the wheels.
In some of the electric and hybrid electric vehicles mentioned above, an electric drive module (EDM) is used to generate and deliver tractive power to a pair of wheels. The electric drive module may include an electric traction motor, a final drive assembly including a differential unit that is adapted for connection to the wheels, and a reduction gearset directly coupling an output component of the traction motor to an input component of the differential unit. The reduction gearset may be based on a layshaft configuration or a planetary configuration for the purpose of providing a desired speed reduction and torque multiplication between the traction motor and the differential unit. Thus, the electric drive module is essentially a single-speed or “direct drive” transaxle that can be adapted to drive either the front wheels or the rear wheels of the vehicle.
In conventional vehicles, some type of torque modulator or torque damper is used, such as a clutch or a torque converter, to dampen the torque transfer between the powertrain and the wheels. However, in vehicles equipped with an electric drive module, the wheels and the drivetrain are always coupled together. As such, the electric drive module must be engineered to withstand the large torque transients and torque reversals that are anticipated to occur during braking events and/or in response to the vehicle travelling over severe road conditions. During these events, the rotary components of the reduction gearset and the electric motor are subjected to unmatched wind-up velocities induced by the wheels which can cause torque loads that are significantly larger than the maximum torque produced by the electric motor. To avoid damage, the components of the electric drive module must be sized to accommodate such excessive peak loading conditions, thereby increasing mass and cost. In addition, adaptive motor control algorithms may need to be implemented into the control system associated with the electric drive module to assist in counteracting the mismatch in torque loads and directions.
In view of the above, it would be beneficial to provide technology that addresses and overcomes these issues so as to facilitate the design and manufacturer of electric drive modules for electric and hybrid electric vehicles having optimized mass and sizing characteristics as well as improved operational functionality.